The present invention relates to a process for the production of an absorbing polymer structure, an absorbing polymer structure obtainable by this process, an absorbing polymer structure, a composite, a process for the production of a composite, a composite obtainable according to this process, foams, moulded articles, fibers, sheets, films, cables, sealing materials, liquid-absorbing hygiene articles, carriers for plant growth-regulating and fungal growth-regulating agents, packaging materials and soil additives or building materials containing these absorbing polymer structures or this composite, as well as the use of this absorbing polymer structure or this composite in foams, moulded articles, fibers, sheets, films, cables, sealing materials, liquid-absorbing hygiene articles, carriers for plant growth-regulating and fungal growth-regulating agents, packaging materials, soil additives or building materials.
Water-absorbing polymers are used in modem cable production in order to protect these cables against the penetration of water and the damage resulting therefrom. Such water damage occurs in particular if the outer sheathing or the structure of the cables is damaged by mechanical action or by excessive bending. The water can penetrate through the openings that are thereby formed and, if no water-absorbing polymer is present, the structure of the cables is permanently affected to such an extent that the functional integrity of the cables is no longer guaranteed. Another possible way in which water can penetrate is if the cables are repeatedly exposed to water vapour, which penetrates through the insulation or the outer sheathing and is then deposited as condensation in the internal structure of the cables. Such condensation leads particularly in the case of electrical cables to the occurrence of leakage currents that adversely affect the functional integrity of the electrical cable or to electrical short circuits that destroy the overall structure of the cables.
In conjunction with the use of water-absorbing polymers in cable manufacture it is preferred that these water-absorbing polymers have good blocking properties in addition to a good gel stability.
Good blocking properties exist when the penetration of a test liquid through the absorbing polymer is as low as possible. Accordingly the good blocking properties mean that the penetrating water can be retained as long as possible in the absorbing polymer and in this way the penetration of the water to the further part of the cable structure is delayed.
Also, these water-absorbing polymers require a high absorbency for penetrating liquids and must swell rapidly in order to fill effectively and completely the cavities in the cable when moisture penetrates. Small, porous particles swell rapidly but are not sufficiently stable. Similarly, although a low crosslinking density leads to a high absorbency, the stability is in turn reduced.
Examples of water-absorbing polymers used up to now include crosslinked, partially neutralized polyacrylates, crosslinked, neutralized graft polymers of acrylic acid on starch, saponified, crosslinked copolymers of vinyl acetate and acrylic acid esters, and neutralized crosslinked copolymers of isobutylene and maleic anhydride.
U.S. Re Pat. No. 32,649 discloses a conventional water-absorbing polymer which, although it exhibits good blocking properties, nevertheless has a gel stability that is not satisfactory for cable manufacture.
DE 40 20 780 furthermore discloses a water-absorbing polymer which, in contrast to the aforementioned conventional water-absorbing polymer, has been modified by a post-crosslinking step following the synthesis of the conventional polymer. Although this post-crosslinked polymer exhibits a gel stability that is acceptable for cable manufacture, nevertheless the blocking properties of this post-crosslinked polymer are not suitable for cable manufacture.
The object of the invention is in general to overcome the disadvantages inherent in the prior art.
A further object according to the invention is to provide a water-absorbing polymer that is suitable for cable manufacture.
In addition another object according to the invention is to provide a water-absorbing polymer that exhibits blocking properties suitable for cable manufacture as well as a stability that is likewise appropriate for cable manufacture.
Yet a further object of the invention is to provide a water-absorbing polymer that is suitable, apart from cable manufacture, also for use in liquid-absorbing hygiene articles such as sanitary towels or diapers.